In recent years, devices that detect weak light have been widely introduced primarily in medical sites and research sites. In such devices, as a detection unit to detect the weak light, a relatively expensive photomultiplier tube is often used.
Further, a device that detects weak light using an imaging element such as a complementary metal oxide semiconductor (CMOS) image sensor that can be manufactured at a low price instead of a photomultiplier tube has been proposed (for example, see Patent Document 1).